Search

International audience; The paper presents a single-crystal ESR study of a series of pristine and X-ray irradiated (TMTTF)2X salts, where TMTTF is tetramethyltetrathiafulvalene and X is either a centro-symmetrical (SbF6 and Br) or a non-centro-symmetrical (ReO4, ClO4, BF4, SCN and NO3) monovalent anion. Besides standard line-width and spin-susceptibility measurements, the analysis of the asymmetry of the ESR line shape allows to obtain simultaneous information on the electrical conductivity. This whole set of data is used to determine the charge and spin gaps related to the charge ordering (CO) and anion ordering (AO) ground states and their evolution as a function of X-ray irradiation damages. We show in particular that the sensibility of (TMTTF)2X salts to irradiation depends upon the nature of the anion X and that the CO ground state is drastically affected by irradiation damages at the difference of the AO ground state. We also present evidence of a CO transition and of a decoupling between the AO transition and the opening of a spin gap in (TMTTF)2NO3.

International audience; A sharp maximum in the temperature dependence of the relaxation time obtained from low-frequency permittivity measurements is found in the quasi-one-dimensional conductor at a temperature of 101. This maximum is associated with the second-order phase transition into a charge-ordered state of Wigner type. The character of relaxation processes above and below this phase transition is discussed.

We have measured the temperature dependences of the conductance G and the dielectric permittivity e ′ of the (TMTTF) 2 SbF 6 compound under a moderate pressure. The maximum of G ( T ) associated with the Mott–Hubbard localization disappears under pressure. With increasing pressure the peak in e ′( T ), corresponding to the charge ordering (CO) phase transition, shifts to lower temperatures and broadens. At pressures above 0.24 GPa, e ′( T ) becomes strongly frequency dependent. These modifications are explained in the frame of the extended Hubbard model and a slowing down behavior.

CETBz-TTF (4,5-bis(cyanoethylthio)benzo-tetrathiafulvalene) and CESBz-TTF (4,5-bis(cyanoethylseleno)benzo-tetrathiafulvalene) 5 have been synthesized from cyano precursor via a cross-coupling reaction. Radical salts with paramagnetic Cu(II) complex anions, such as (CETBz-TTF)2CuCl4 6 and (CESBz-TTF)2CuCl4 7 have been prepared. X-ray crystal structure and physical properties of these new compounds are presented.

We report the first extensive study of longitudinal (ρ a ) and transverse (ρ c ) transport properties versus temperature of the organic quasi one dimensional conductor TMTTF2PF6 over the pressure domain extending from ambient up to 26 kbar. The dimensional cross over observed around 14 kbar separates a 1D region dominated by the Mott-Hubbard gap with activated transport at low pressure from a 3D domain where the temperature range of the metallic behavior, extends up to room temperature along the chains and is progressively increased towards high temperatures in the c direction. In the 1D regime, the different activations obtained from ρ a (T) and ρ c (T) data suggest two different modes of conduction in the longitudinal and transverse directions.

Within the generic (pressure, temperature) phase diagram of (TM) 2 X compounds, we have investigated the crossover between the spin density wave and superconducting ground states by transport measurements under pressure. Superconductivity is reported for the first time in (TMTTF) 2 BF 4 below 1.38 K, in the pressure range 33.5–37.5 kbar, and coexists with the spin density wave phase, present alone at lower pressure. Differential resistance measurements support the idea of a phase segregation with the proportion of the superconducting phase (related to the measured critical current) increasing with pressure.

The synthesis of series of tris- and tetrakis-tetrathiafulvalene (TTF) has been carried out by using complementary routes involving deprotection-alkylation methods of mono or dithiolates. The electron donor ability of these new compounds has been measured by cyclic voltammetry (CV) and the square wave (SQW) technique. All the products exhibit a donating power similar to those found for TTF derivatives such as TMTTF and BEDT-TTF known to lead to conducting salts. Most of these donors have been converted by galvanostatic electrosynthesis into perchlorate and hexafluorophosphate salts. These salts have been found semi-conducting.

A detailed thermodynamical investigation of the quasi-one-dimensional sulphur-based organic salts (TMTTF)2PF6 and (TMTTF)2Br is presented in the temperature range from 30 mK to 7 K. In this part (part I), we consider the general aspects of the low-temperature specific heat of these materials in relationship with their ground states and we compare them with those previously measured for selenium members of the same family. All these compounds exhibit very similar thermodynamical behaviour, despite a variety of electronic ground states: spin-Peierls for (TMTTF)2PF6, commensurate antiferromagnetic spin modulation for (TMTTF)2Br, incommensurate spin-density wave for (TMTSF)2PF6 (TMTSF≡tetramethyltetraselenafulvalene). We show that the low-energy excitations which are predominant below 1 K have a similar character to that observed in glassy systems, at least on short timescales of measurements. The dynamical aspects of the non-equilibrium thermodynamics will be presented separately in the following part (part II).

Conductivity and permittivity of the quasi-one-dimensionsional organic transfer salt $(\mathrm{TMTTF}{)}_{2}{\mathrm{PF}}_{6}$ have been measured at low frequencies ${(10}^{3}\char21{}{10}^{7}\mathrm{Hz})$ between room temperature down to below the temperature of transition into the spin-Peierls state. We interpret the huge real part of the dielectric permittivity (up to ${10}^{6})$ in the localized state as the realization in this compound of a charge ordered state of Wigner crystal type due to long-range Coulomb interaction.

Direct evidence of a new phase transition at TCO = 100.6 K in the organic quasi-one-dimensional (TMTTF)2AsF6 salt has been obtained from conductivity and dielectric permittivity measurements. This phase transition is assigned to a charge-ordered state (4kF charge density wave of Wigner type) due to charge-induced electron-electron interactions.

We present a study, of the slow dynamics in the heat relaxation at very low temperature (T < 1 K) in the nominally commensurate SDW compound (TMTTF) 2 Br, that we compare to the incommensurate SDW-(TMTSF) 2 PF 6 . Instead of a broad distribution of relaxation times g(log τ) in the PF 6 salt, the dynamics in the Br salt reveals almost discrete bands in the relaxation spectrum. A saturation towards equilibrium is reached very rapidly (within ∼ 20 mn) at T ∼ 100 mK in comparison with PF 6 (more than 10 hr for the same temperature).

We present c-axis resistivity measurements performed on the organic conductors and under pressure. The aim is to probe the density of states of quasi-one dimensional compounds the high temperature properties of which are those of a Luttinger liquid. It is found that the 1-D Luttinger description breaks down below a specific pressure-dependent temperature, giving rise to a transient regime. The Fermi liquid behaviour is however restored at low temperature i.e. around 10 K, as evidenced by NMR measurements. Accordingly, two different energy scales 100 K and 10 K are required to get a fair understanding of all observed physical phenomena. Our interpretation supports the picture of a power law exponent for the correlation functions of the order of 0.25–0.30.

We report the transverse magnetoresistance measurements at ambient pressure in the organic conductor (TMTTF)2Br in the temperature range between 4.2 K and 40 K and in magnetic fields up to 8.5 T. We have found isotropic, negative and temperature dependent magnetoresistance which becomes negligible, close to 40 K. We interpret the observed behaviour within the picture of strongly correlated quasi-one dimensional systems.

Hall effect measurements of the organic conductor (TMTSF) 2 NO 3 at low temperatures (1.8 ≤ T ≤7 K) and high magnetic fields (H ≤ 8.5 T), are reported. The large Hall coefficient R H indicates the semimetallic nature of the spin density wave (SDW) ground state, whereas its positive sign shows the dominance of the hole carriers. Both R H and resistivity increase with decreasing temperature, which suggests the possibility that the carrier concentration is reduced as the temperature is lowered. The field variation of Hall resistance R xy deviates from the linear dependence for T ≤ 4 K and H ≥ 3 T. This could be interpreted not only by the temperature induced change in the number of carriers or anisotropy of their mobilities, but also by the possibility that the SDW state might change with the applied magnetic field.

Conductivity and permittivity of the quasi-one-dimensional conductor (TMTTF) 2 SbF 6 , have been measured at low frequencies (f= 10 2 ∼ 10 7 Hz) under several pressures (P= 0 ∼ 0.5GPa). The real part of the conductivity has a maximum at Tm due to charge localization of Mott-Hubbard type. Below T m , the real part of the permittivity (e') shows a sharp peak with the magnitude in the order of 10 5 ∼ 10 6 . It has been suggested that the anomaly of e' is due to a charge ordering (CO) phase transition. We found that the CO transition temperature decreases with pressure. Above 0.25GPa, the temperature dependence of e' is strongly dependent on frequency in the frequency range of measurements. We will discuss the pressure effect on the CO phase transition in (TMTTF) 2 X family.

The metallic state of a high-quality (TMTTF)2 Br sample was stabilized under a pressure of 26 kbars. The magnetoresistance of the system was then studied up to 20 teslas for a field rotating in the least-conducting plane. The anisotropy of the magnetoresistance was found to be different from what had been observed in the TMTSF family. For a field along the c-axis, a small kink in the magnetoresistance at H = 13 T is detected which may be the first signature of the appearance of the FISDW states.

The study of the magnetoresistance in the organic quasi-one-dimensional conductor (TMTSF)2NO3 at a pressure (8 kbar) exceeding the critical pressure required for the stabilization of a conducting state at low temperature has revealed the existence of quantum oscillations with a frequency of 190 T in good agreement with an extended Huckel-type calculation of the band structure. Unlike other members of the (TMTSF)2X series the ambient pressure SDW ground state in (TMTSF)2NO3 can be understood in terms of an instability involving the nesting of 2D semi-metallic Fermi surfaces.

Transverse magnetoresistance of the organic conductor (TMTSF) 2 NO 3 has been measured at ambient pressure, in fields up to 37T and in the temperature range 2–77K. For field along the lowest conductivity axis (c∗), the magnetic field is found to increase the SDW transition temperature, in agreement with theoretical predictions for SDW phase with imperfect nesting. On the other hand, two series of quantum oscillations, with frequency of 63T and 246T respectively, are observed in the 2–10K range. Both series are connected to the SDW transition but cannot be accounted for by Shubnikov-de Haas model. Anisotropy of these oscillations is studied at 4.2K.

We show that the newly discovered phase transitions in (TMTTF)2X (X=PF6, AsF6, SbF6, ReO4) are characterised by a huge divergent peak in the low frequency dielectric constant. These phase transitions can be explained by combined effect of charge disproportionation on TMTTF molecules and the uniform shift of anions, yielding thus a macroscopic ferroelectric polarisation. Anion ordering transition, which occurs for non-centrosymmetrical anions, has a specific effect depending on the distortion vector: it destabilises the ferroelectric state in the (TMTTF)2ReO4 and brings an antiferroelectric character to the transition in (TMTTF)2SCN.

The transverse magnetoresistance of the Bechgaard salt (TMTSF)[sub 2]NO[sub 3] has been measured up to 37 T at ambient pressure in the temperature range from 2 to 77 K. When the magnetic field is parallel to the lowest conductivity direction [ital c][sup *] and for temperatures higher than [similar to]12 K, the data can be accounted for by a power law, the exponent of which decreases as the anion ordering takes place. At lower temperatures, the magnetic field increases the spin-density-wave (SDW) transition temperature, in overall agreement with theoretical predictions for the imperfect-nesting case. Two oscillation series, both linked to the SDW state, have been observed in the 2--10 K range. Their temperature-independent frequencies, measured from 2 to 8 K, are at (63[plus minus]2) and (248[plus minus]5) T, respectively. These oscillations have been studied (at 4.2 K) as a function of the field direction. They were found to deviate from the two-dimensional model since, in particular, their behavior differs according to whether the field is tilted on one side of the [ital c][sup *] direction or on the other. The oscillation data are discussed on the basis of recent calculations of Yakovenko.

We have observed a clear series of fine structures superposed on the angular dependence of the transverse magnetoresistance in the semimetallic spin-density-wave state of the organic conductor (TMTSF${)}_{2}$${\mathrm{NO}}_{3}$. They appear at the positions defined by the strength of the field component parallel to the least-conduction direction (B cos \ensuremath{\theta}\ensuremath{\simeq}const). An observed asymmetry in the magnitude is due to the striking angular dependence of the oscillations amplitude. The frequency of the oscillations (${\mathit{B}}_{\mathit{S}}$=63 T) is close to the frequency of the field-induced spin-density-wave transitions found in the other Bechgaard salts. This oscillatory phenomenon is considered to result from the orbit quantization inside the closed parts of the Fermi surface which are due to the 2${\mathit{k}}_{\mathit{F}}$ anion ordering together with the imperfect spin-density-wave nesting.

We report magnetotransport measurements in the quasi one dimensional (Q-1-D) organic conductor (TMTTF) 2 Br at pressures up to 26 kbar, down to 0.45 K in magnetic fields up to 19 T along the c * direction. It is found that a superconducting ground state is stabilized under 26 kbar at T c =0.8 K. No magnetic field induced spin density wave (FISDW) transitions are observed below 19T unlike other Q-1-D superconductors pertaining to the selenium series. The computed amplitude of the interchain coupling along transverse directions is unable to explain the missing FISDW instability

Methods have been developed for the synthesis of novel intercalates of graphite, metal dichalcogenides (MY2: M = Ti, Ta; Y = S, Se; M = Nb; Y = Se, Te) and metal halides CuCl2; MBr2: M = Ni, Cu, Cd; CdI2). Aromatic hydrocarbons (pentacene (PEN), tetracene (TET), anthracene (ANT), 9,10-dichloroanthracene (DCA), and 9,10-dibromoanthracene (DBA)) have been intercalated into graphite, and PEN, TET, ANT have been intercalated into the metal dichalcogenides. Dibenzotetrathiafulvalene has been intercalated into MY2 (M = Ti, Ta; Y = S, Se). In addition, C60 intercalates of TaS2 and graphite have been prepared. Tetracyanotetrathiafulvalene was intercalated into 5 metal dihalides, forming the first known intercalates of these materials. The intercalates were structurally analyzed by X-ray powder diffraction, and the compositions determined experimentally. For all intercalates, the observed stoichiometries were in good agreement with those predicted from the X-ray data. The results of resistivity and magnet...

New unsymmetrically substituted tetrathia- and dithiadiselenafulvalenes of the bis-ethylenedioxy-tetrathiafulvalene (BEDO-TTF) type have been prepared and characterized. Some of their radical cation salts have also been synthesized.

We have used electric-field-dependent measurements to probe the magnetic-field dependence of the phase-coherence length in the spin-density-wave (SDW) state of the organic conductor tetramethyltetraselenafulvalinium nitrate (TMTSF${)}_{2}$${\mathrm{NO}}_{3}$. The threshold electric field increases if a magnetic field is applied in the plane perpendicular to the highly conducting axis. The magnitude of the increase is angle-dependent and vanishes when the field is applied along the intermediate-conductivity axis. This behavior results from a reduction of the phase-coherence length of the SDW with strongly imperfect nesting in a magnetic field.

We briefly remind the synthesis of a series of new dimethyltetrachalcogenofulvalenes (I) bearing one or two hydroxymethyl group(s) as substituent(s). The preparation and characterization of their radical cation salts are also reported. The electrical conductivity on compressed powder pellets and their FTIR spectra are, in some cases, given.

We describe the synthesis of a series of new unsymmetrically substituted tetraselena- and dithiadiselenafulvalenes bearing one or two functionalities such as diethylacetal, formyl or hydroxymethyl groups. The physical properties and spectroscopic data of these new π-donors are reported.

International audience; The detailed synthesis of a new series of conjugated TTF ligands with nitrogen-based aromatic heterocycle are presented. In all these molecules, trimethyl-TTF or TTF skeleton are bridged to the nitrogen aromatic ligand through a conjugated spacer such as ethenyl or phenylethenyl unit. Their electrochemical characterization as well as the crystal structure of one of these compounds is given.

6 pages; International audience; We report a preliminary study of two novel complexes combining a paramagnetic transition metal (Cu(II)) and a cyclophane-type TTF-bipyridine ligand TTF-bipy = (cis)2,7-bis(pentylsulfanyl)-3,6- [2,2-bipyridine-bis(4,4-methanediyl)bis-sulfanyl]tetrathiafulvalene. The syntheses of the complexes Cu(hfac)2(TTF-bipy) (hfac = hexafluoroacetylacetonate) and Cu(NO3)2(TTF-bipy)·H2O are reported. The results of single-crystal EPR measurements are discussed on the basis of structural features deduced from preliminary X-ray diffraction data and indicate that these neutral molecular complexes behave as isolated paramagnetic units.

We report the synthesis of a new series of dithiadiselenafulvalenes. We describe the electrical conductivity and the FTIR spectra of both their radical cation salts and their charge transfer complexes with TCNQ.

The preparations, X-ray crystals structures, optical, ESR and magnetic characterizations of new Organic-donor Inorganic -Acceptor salts are presented. The [BEDT-TFF]2M6O19 ( M = Mo ( 1 ) and W ( 2 )) present orthogonalized fully oxidized and diamagnetic organic dimers. The structure of (TPh-TTF)2W6O19 (3) shows isolated and fully oxidized organic molecules. Organic stacks made of phenyl-rings and central TTF parts are also observed in the latter compound.

International audience; The title compound, C30H28N2S16, is a precursor to hybrid magnetic materials. The complete molecule is generated by a crystallographic inversion centre. In the crystal structure, the TTF core is not planar and adopts a chair conformation; the two C3S2 rings are folded around the S center dot center dot center dot S hinges, the dihedral angles being 17.14 (8) and 13.46 (7)degrees. There is a short S center dot center dot center dot S contact [3.4863 (14) angstrom] in the crystal structure.

This paper is a review of the electrical properties of organic materials containing unsymmetrically substituted TTF and TSF. Two series of these donors were prepared using a Wittig-type reaction with the sulfur compounds, and a cross-coupling method with their selenium analogues. Their radical-cation salts were synthesized by electrochemical oxidation and their charge-transfer complexes were obtained chemically using TCNQ and its 2,5-dimethylated derivative DMTCNQ. The crystal structures were determined by X-ray diffraction when single crystals were obtained. The electrical properties are correlated to the structural data.

International audience; Une des stratégies possibles pour la synthèse de matériaux moléculaires conducteurs de l'électricité basée sur unsymmetrically substitué tetrathiafulvalenes implique l'utilisation d'un précurseur portant cyanoethylsulfanyl groupes attachés à la tetrathiafulvalene (TTF) de base. The title compound, C 16 H 16 N 2 S 6 , is such a precursor. Le titre composé C 16 H 16 N 2 S 6, est un précurseur. The two cyanoethylsulfanyl groups are attached to the two adjacent C atoms of one of the two C 3 S 2 rings of the TTF core and protrude on both sides of the molecule. Les deux groupes sont cyanoethylsulfanyl fixé aux deux atomes adjacents C de l'un des deux C 3 S 2 anneaux de base et le Fonds saillie sur les deux côtés de la molécule. In the crystal structure, the TTF core is not planar and adopts a boat conformation; the two C 3 S 2 rings are folded around the S Dans la structure cristalline, le Fonds de base ne sont pas planes et adopte un bateau de conformation; Les deux C 3 S 2 anneaux sont pliés autour de la S S hinges, the dihedral angles being 12.19 (6) and 22.70 (4)°. S charnières, les angles de dièdre étant 19/12 (6) et 22.70 (4) °. There are no unusual intermolecular contacts in the solid state. Il n'ya pas inhabituel intermoléculaire des contacts à l'état solide. The crystal studied was a partial inversion twin, with contributions of 0.72 (4) and 0.28 (4) for the two twin domains. Le cristal a été étudié partielle inversion de jumeaux, avec des contributions de 0,72 (4) et 0.28 (4) pour les deux jumeaux domaines.

International audience; By using two different routes, series of new bis- and tris-TTF, containing in their linker function(s) able to generate supplementary interactions in the resulting materials, have been prepared. The first route based on deprotection-realkylation strategy allowed to introduce alcohol and ketone functions. The second way, using acid chloride and hydroxy-TTF, allowed to include ester function in the linker. The electron-donating ability of this series of TTFs has been determined by CV and by SQW.

Interlayer magnetoresistance of the Bechgaard salt (TMTSF)$_2$NO$_3$ is investigated up to 50 teslas under pressures of a few kilobars. This compound, the Fermi surface of which is quasi two-dimensional at low temperature, is a semi metal under pressure. Nevertheless, a field-induced spin density wave is evidenced at 8.5 kbar above $\sim$ 20 T. This state is characterized by a drastically different spectrum of the quantum oscillations compared to the low pressure spin density wave state.

Two asymmetric tetrathiafulvalenes of BEDO-TTF type have been prepared: EDO-DMTTF: I and EDODT-DMDSF: II. A series of radical cation salts of I have been obtained and their electrical conductivity measured. In addition crystal structure of EDO-DMTF 2 X (X=NO 3 − ; ReO 4 − ) are now given.

We report the observation of superconductivity in the spin-Peierls Fabre salt (TMTTF)2PF6 from pressure dependent electrical transport measurements above a threshold of 4.35 GPa. The data complete the sequence of ground states of this compound in the temperature and pressure plane adducing an empirical basis to the universal character of the phase diagram of the Fabre salts and their selenide analogues, the Bechgaard salts. The structure of the phase diagram at the approach of the crossover between spin-density wave and superconducting states is compared with the results of scaling theory of the interplay between both electronic instabilities under pressure. The comparison supports the view that magnetism and superconductivity in these compounds have a common electronic origin.

Summary form only given. We studied the Fermi surface of the organic conductor (TMTSF)/sub 2/NO/sub 3/ through the measurements of magnetic quantum oscillations. Two different families of oscillations are observed. Well defined Shuvnikov-de Haas(SdH) oscillations with frequency of ca. 60T can be observed below 8K and above 6T at the ambient pressure. The higher frequency oscillations reported elsewhere is not visible be low 12T. The angular magnetoresistance does not show any structure neither at Yamaji's magic angles nor at Lebed's resonance condition. Only the SdH oscillations for the field scaled by Cos /spl theta/ are added and easily separated. Under a pressure of 10kbar, different oscillations with frequency of ca. 200T is observed above 10T at 450mK. Even though it is the same frequency as so called rapid oscillations observed in other Bechgaard salts, angular dependence of oscillation frequency does not follow the simple cosine law contrary to that of (TMTSF)/sub 2/CIO/sub 4/. The amplitude of oscillations depend very oddly with sample orientation, too. Both suggest that the electron structure at low temperature is strongly modified upon application of pressure which may explain the absence of superconductivity and the field-induced spin-density waves. The angular magnetoresistance shows actually three maxima at angles which are not determined from the known theories.

Summary form only given. We report a study of the transverse magnetoresistance of the organic conductor (TMTSF)/sub 2/NO/sub 3/ at ambient pressure, in fields up to 37T and in the temperature range from 2 to 77K. For field along the lowest conductivity axis (c/sup */), two series of quantum oscillations, with temperature independent frequencies of 63T and 247T respectively, are observed in the 2-10K temperature range. The oscillations amplitude of both series decreases when the temperature departs from nearby 4K. Both series are connected to the SDW transition but cannot be accounted for by SdH model. The data is tentatively interpreted, in this temperature range, within the framework of magnetic breakthrough and quantum interferences. The anisotropy of these oscillations is also studied at 4.2K. On the other hand, the magnetic field is found to increase the SDW transition temperature, in agreement with theoretical predictions for SDW phase with imperfect nesting.

Summary form only given. We present preliminary data on the low temperature magnetoresistance of (TMTSF)/sub 2/AsF/sub 6/, investigated in a high magnetic field of 37T at liquid helium temperature in the ambient pressure spin density wave state of the compound. Starting around 15T a single series of fast oscillations periodic in I/B is visible with a fundamental frequency very close to 200T. The AsF/sub 6/ salt is believed to have physical properties very similar to those of PF/sub 6/. However this frequency is substantially lower than the 230T measured in PF/sub 6/. More detailed experiments concerning the angular and temperature dependence of both oscillatory and background magnetoresistance are in progress.

We present the influence of a transverse magnetic field on the spin-density wave (SDW) ground state of the organic conductor (TMTSF) 2 NO 3 . Magnetic field increases the single-particle activation energy. A finite magnetic field (H C ) induces discontinuities in the magnetoresistance behaviour and its value is temperature dependent. The threshold electric field (E T ) for the SDW sliding increases in a magnetic field. All observed effects are strongly angle-dependent indicating that they are determined by the magnetic field component along the least-conduction (c * ) direction. We discuss these results in the framework of a theoretical model for the SDW with large imperfect nesting

We report a study of the transverse magnetoresistance properties in the spin-density wave (SDW) phase of the organic conductor (TMTSF) 2 NO 3 at temperature down to 1.8 K and in magnetic field up to 6 tesla. The transverse magnetoresistance shows large effect and is highly anisotropic. We analyze our data in the framework of recent theoretical calculations by K. Maki. We suggest that the SDW with large imperfect nesting together with a periodic anion potential might be responsible for the magnetic field effects

We report a study of the transverse-magnetoresistance anisotropy in the spin-density wave phase of the organic conductor (TMTSF)2NO3 at temperatures down to 1.8 K and in fields up to 6 tesla. The transverse magnetoresistance is highly anisotropic and obeys a temperature- and angular-dependent power law behaviour: DELTArho/rho congruent-to H(n) (1 less- than-or-equal-to n < 2). The indication of a possible field-induced SDW phase is discussed. We suggest that the SDW with large imperfect nesting together with a periodic anion potential might be responsible for the observed magnetic-field effects.